Light-emitting diodes (hereafter abbreviated as LEDs), which are compound semiconductors, have been widely utilized as light-emitting devices, taking advantage of characteristics such as long operating life and compact size. Furthermore, as a result of the development of LEDs which emit blue light using, for example, gallium nitride based compound semiconductors, the commercialization of white light and pseudo-white light-emitting devices has advanced, and high luminance and high output light-emitting devices, for which LED heat dissipation methods have been devised, have been commercialized as well. In addition, since light-emitting amount is limited by one LED element, an assembled semiconductor light-emitting device is known in which a number of LED elements are mounted on a small mounting area to achieve a large amount of light.
For example, in Japanese Laid-open Patent Publication No. 2007-115928, a semiconductor light-emitting device is disclosed which has first LED elements mounted on a substrate, and a second LED element mounted above the first LED elements in a laminated and shifted state, and each of the first LED elements has p and n electrodes on the upper surfaces thereof, and the second LED element has p and n electrodes on the lower surface thereof. In this semiconductor light-emitting device, the p electrode of the second LED element is attached to the n electrode of one of the adjoining first LED elements, and the n electrode of the second LED element is attached to the p electrode of the other of the adjoining first LED elements. Since the second LED element is hereby mounted in the laminated and shifted state relative to the first LED elements, the mounting area of the LED elements can be reduced and the luminous flux density per unit area can be improved, thus enabling miniaturization of the entire package and improvement of luminosity.
In addition, in Japanese Laid-open Patent Publication No. H10-173225, a semiconductor light-emitting element is disclosed in which three or more of a first LED element and a second LED element are alternately lined up and connected in series into a straight-line shape. In this semiconductor light-emitting element, the first LED element has an n-side electrode and a p-side electrode, and the second LED element has semiconductor layers laminated on the front surface side of a transparent substrate, has an n-side electrode and a p-side electrode, and is disposed so that the side on which the electrodes are provided faces the opposite direction of the first LED element. With the first and second LED elements, the n-side electrodes or the p-side electrodes on the different sides are directly attached to each other. Since there are no gaps between the LED elements, this semiconductor light-emitting element can achieve a size reduction of approximately one-half compared with a light-emitting element having the same amount of light and the same number of LED elements connected therein.
In addition, in Japanese Laid-open Patent Publication No. 2009-94294, a semiconductor light-emitting device is disclosed which has multiple LED elements stacked in two layers on a circuit board, and which is configured such that upper layer LED elements and lower layer LED elements are alternately connected in series through bumps. The circuit board of this semiconductor light-emitting device has a recessed portion for accommodating the LED elements, and the lower layer LED elements are accommodated in the recessed portion. All or some of the upper layer LED elements are electrically connected through bumps to a wiring pattern formed on the circuit board. By such a configuration, the heat generated by the LED elements can be dissipated through the circuit board. In addition, since the upper and lower layer LED elements and the wiring pattern formed on the circuit board are connected without using bonding wires, the light source unit can be made compact, which makes it possible to reduce the size of the semiconductor light-emitting device and increase the lighting intensity of the illumination unit.